The present invention relates to a storage system and a copying method implemented between plural geographically separated sites.
Continuity of an IT (information technology) system having a host computer and a storage system and reliability of data stored in the storage system have become very important as IT has become popular. There is an increasing demand for protecting data from unexpected accidents such as terrorism, natural disaster, etc. Remote copying by a storage system is one of techniques supporting such a demand. Remote copying is a technique in which update data stored in a copy source volume included in a copy source storage system is copied to a copy destination volume included in a copy destination storage system so that the data can be conserved in the copy destination volume even when an event of making the data disappear from the copy source volume (e.g. natural disaster such as a fire, an earthquake, a flood, etc. or power failure) occurred.
As disclosed in U.S. Pat. No. 7,225,190, update data issued from a host computer to a storage system is copied by the storage system so that one data is stored in the storage system and the other copied data is transferred to a remote storage system and stored in the remote storage system. This procedure permits the storage system to be recovered by use of the data stored in the remote storage system even after some failure occurred in the storage system because of disaster or the like.
Remote copying disclosed in U.S. Pat. No. 7,225,190 is a technique called synchronous remote copying. In this technique, unless the data issued from the host computer to the storage system is completely stored in the remote storage system, the host computer does not receive a report of completion of the data. This procedure guarantees the data to be stored in the remote storage system if a report of completion of the data has been already received by the host computer.
On the other hand, an asynchronous remote copying technique has been disclosed in U.S. Pat. No. 7,191,303. According to U.S. Pat. No. 7,191,303, a report of completion of update data issued from a host computer to a storage system is received by the host computer as soon as the data is received by the storage system. The data received by the storage system is copied asynchronously with processing of the completion report so that the copied data is transferred to a remote storage system and stored in the remote storage system. This procedure permits the host computer to perform data input/output processing independent of the data transfer distance between the storage systems.
The achievement of remote copying by storage systems can reduce the copying load imposed on the host computer but needs monitoring and operating of remote copying from a management computer or the host computer. For this reason, each storage system holds information of a copying state (e.g. as to whether copying is operating normally, whether initial copying is currently made, whether copying is suspended for some reason, etc.) for a pair of the copy source volume and the copy destination volume and transmits the copying state to the management computer or the host computer. The management computer or the host computer refers to the copying state to monitor the pair whether failure occurred or not.
On the other hand, remote copying uses a path technique for transmission/reception of data between storage systems. For example, the path technique has been disclosed in JP-A-2001-109699. In JP-A-2001-109699, logical communication lines (referred to as logical paths) are formed on a physical communication line (referred to as physical path) coupled between storage systems geographically separated from each other so that data for remote copying is transmitted/received on the logical path. This procedure permits plural logical paths to be formed on a physical path even when plural remote copying processes are performed between the storage systems, so that the physical path can be shared to the plural remote copying processes.
Assume now that failure occurs in the physical path when plural remote copying processes are being executed between storage systems.
According to U.S. Pat. No. 7,225,190, there is no data transmission between storage systems unless the host computer issues update data to any storage system. For this reason, the storage system cannot detect the physical path failure caused by communication line failure unless the host computer issues update data.
According to U.S. Pat. No. 7,191,303, in asynchronous remote copying, even when there is failure in the physical path, an administrator cannot detect the physical path failure as a remote copying failure immediately because data transmission is temporarily reserved in the storage system on the data transmission source site.
According to JP-A-2001-109699, because plural and arbitrary logical paths can be formed on one physical path so that data for any remote copying can be received/transmitted on each logical path, it is impossible to specify the remote copying affected by failure in the physical path.
As described above, in the related art, it was difficult to monitor the physical paths from the viewpoint of remote copying.